Caching Explained: A Simple Guide to Why You´re Undercounting Your Traffic by up to 40%!
Browser- and proxy-caching, and its effect of understating actual viewership rates by up to 40%
, is very relevant to anyone who is selling advertising space on a per-view (i.e. CPM) basis. Anyone using traditional server logs to count banner impressions is undercharging their advertisers by up to 40%.
This white paper covers:
What Is Browser- and Proxy-Caching?
The Internet is slow. Really slow. Therefore the less information you need to send through it, the better.
Imagine trudging to the library every single time you wanted to refer to a favorite magazine article. Of course what you end up doing instead is keeping a photocopy of the article on hand (say, in your desk drawer). Whenever you need to refer to it, you pull out your photocopy—a lot
faster than trudging to the library!
The same mechanism is used to "speed up" the Internet experience. Your Browser keeps "photocopies" of pages (and graphics/banners) that it's seen recently. When you use the Back Arrow on your browser, it doesn't request another copy of the page/banner—it just uses the photocopy it already has. When the desk drawer fills up, or if you haven't looked at a photocopy for a while, it's automatically purged.
This is your Browser Cache.
Big ISPs, corporations, and on-line services (like AOL) take this concept one step further...
Their networks are fast. The Internet is slow. So what they do is create a huge desk drawer that is shared by all users who are accessing the Internet through their speedy network. This is a Caching Proxy Server.
When your browser requests a page (or advertising banner) from such a large ISP or on-line service, their
Proxy Server first checks its huge desk drawer to see if it already has a photocopy from someone else who has recently requested the same item. If so, the Proxy Server sends this "photocopy" straight to the browser without going out to the (relatively slow) Internet to ask the originating site for another copy. Otherwise, it goes and gets a photocopy from the originating site and stores it in the shared desk drawer for future reference. A popular site
will get some requests from proxy servers, but a lot less than if there were no proxy-cache.
What The Problem Is, and Why It's Important To You
If you're charging your advertisers based on a per-view (CPM) basis, you owe it to yourself (and your pocketbook) to know how many eyeballs are actually viewing your ads.
As David Gray [VP Marketing,
Off-Road.Com] noted in his postings to I-Advertising article #148, "traditional" server logs do not accurately reflect the number of eyeballs. That's because the server has no way of knowing how many "photocopies" are in circulation. The server only knows about (and therefore logs) requests for originals.
David estimates that his real numbers are 2- to 3-times the amount that his traditional logs show. Yikes—that´s alot of
unpaid advertising exposures!
There are a number of
ways (some better than others) for addressing this under-counting problem:
APPROACH #1: CONFIGURE YOUR WEB SERVER SO THAT OUTGOING PAGES/IMAGES WILL NOT BE CACHED.
While this may solve the under-counting problem on your end, you'll also alienate a lot of your visitors (your site could slow to a crawl under the extra load) and you'll pay $$$more$$$ for bandwidth
(maybe double or triple if David Gray's estimates are accurate). Probably not a good idea :-( However, you *will* get more accurate logs :-)
APPROACH #2: CONFIGURE YOUR WEB SERVER SO THAT ONLY OUTGOING BANNERS WILL NOT BE CACHED.
Tougher to implement, but again slows down the whole experience
. You want your banners to load instantly (preferably before anything else on the page!) and this approach will cause the opposite effect. Your banner will be the last thing on the page to load :-( but your bandwidth charges won't go through the roof :-) Better than approach #1 but still not the best.
APPROACH #3: USE A DEDICATED CACHE-RESISTANT "IMPRESSION" TRACKER
For this approach, you don't need to modify your server settings at all. What you do is simply drop an invisible cache-resistant BellaCoola "Tracker" on each of your pages. BellaCoola's Trackers were developed precisely for this purpose and only involve a 52-byte transfer per page view. Your pages (and banners) load just as quickly as before
(because they´re cached), except now you get an exact record of how many eyeballs have seen your ads.
The result is a private, cache-corrected log (including referer) that you can analyze with any 3rd party web analysis package (in fact, we provide you with links to free analyzers and discounts on commercial analyzers). No more having to depend on your web host´s choice of analysis software. And if you move your site, your stats move
Your password-protected BellaCoola Tracker Log will show you exactly how often each advertisement is viewed and the number of sessions that see the ad, regardless of whether the banner (or the rest of the page for that matter) is cached or not. This lets you determine, for instance, the number of people who saw their ad 5 times.
Armed with this information, you can accurately bill your advertisers for the number of times their banners are
actually viewed, rather than just the number of “originals” that are requested from your server (which is typically 40% below the actual viewership rate).
And, because your stats should always be available when you want them, your BellaCoola Tracker Logs are available 24 hours a day, 7 days a week
so you don´t have to worry about your web host deleting your logs before you can analyze them. And we automatically compress (.zip) your BellaCoola Tracker Logs at the end of each month for even faster downloading.
Find out more
about the BellaCoola Tracker Series and how they can help you make your business more profitable.
Better yet, sign up and start getting the whole picture today! You´ll see why we´re the professional´s choice for all-in-one web tracking.
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